Reversible Addition–fragmentation Chain Transfer Polymerization Technique Research Articles

Palladium-SCS Pincer Complexes as Cross-Linking Moieties in Self-Healing Metallopolymers.

Metallopolymers combine properties of metal complexes and polymers and are thus interesting materials for a wide field of different applications. One current major field is the utilization as self-healing polymers, and for this purpose, palladium-SCS pincer complexes are synthesized. Well-defined copolymers featuring those metal complexes in the side chain are obtained using the reversible addition-fragmentation chain-transfer polymerization technique. By the addition of a tetravalent pyridine cross-linkers, reversible cross-linked supramolecular networks are prepared, enabling self-healing properties. By utilizing density functional theory calculations, IR, and Raman spectroscopy, as well as isothermal titration calorimetry, the complex formation, reversibility, and stability are studied. The information of these experiments also enables further optimizations for the design of similar reversible systems in the future.

Tuning the Morphology of an Acrylate-Based Metallo-Supramolecular Network: From Vesicles to Cylinders

This work investigated the morphological behavior of an acrylate-based metallo-supramolecular polymer system. RAFT (reversible addition–fragmentation chain transfer) polymerization techniques were used to synthesize low molar mass, linear prepolymers of n-butyl acrylate and a 2,6-bis(1′-methylbenzimidazolyl)pyridine–acrylate monomer (MeBIP–Ac) of varying concentration (2–10%). This synthesis incorporated a systematic increase of cross-link points (MeBIP ligands) pendent to the polymer backbone. A zinc(II) salt (Zn(ClO4)2) complexed with the pendent MeBIP ligands in a 1:2 ratio to form cross-linked polymers as free-standing films. The morphology of the neat films as well as those with added unbound MeBIP–zinc–MeBIP metal–ligand (ML) complex were characterized using transmission electron microscopy (TEM), HAADF-STEM (high angle annular dark field scanning transmission electron microscopy), energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), energy-filtered TEM (EFTEM), and ...

Synthesis and Characterization of NBR´s by RAFT Technique and their use as Rubber Precursor in ABS Type Resins

Different rubbers based on polybutadiene were synthesized in solution by the reversible addition-fragmentation chain-transfer polymerization (RAFT) technique using 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl] entanoic acid as RAFT agent and 1,1’-azobiscyclohexanecarbonitrile (Vazo-88) as initiator. The results obtained in the polymerization of polybutadiene and poly(butadiene-co-acrylonitrile) (NBR) are discussed in terms of molecular weight distribution, composition and microstructure. Composition of polybutadiene in NBR´s was kept constant along the copolymerization, and the vinyl, cis and trans isomers are shown in values of around 12, 26 and 62% in all cases. Resulting rubbers were used to synthesize acrylonitrilebutadiene-styrene (ABS) type resins through an in situ bulk polymerization. Dynamic-mechanical properties and the morphology were analyzed in all the different ABS resins. In DMA analyses, the rubber component presented two transitions as well as an increase in the magnitude of the transition located around -75 °C, which is explained by the significant amount of SAN occlusions in the morphology, analyzed by TEM.

Synthesis of poly(ω-pentadecalactone)-b-poly(acrylate) diblock copolymers via a combination of enzymatic ring-opening and RAFT polymerization techniques

Herein the first reported preparation of diblock copolymers of the polyethylene-like polyester poly(ω-pentadecalactone) (PPDL) via a combination of enzymatic ring-opening polymerization (eROP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization techniques is described. PPDL was synthesized via eROP using Novozyme 435 as a catalyst and a bifunctional initiator/chain transfer agent (CTA) appropriate for the eROP of ω-pentadecalactone (PDL) and RAFT polymerization of acrylic and styrenic monomers. Chain growth of the PPDL macro-CTA was performed to prepare acrylic and styrenic diblock copolymers of PPDL, and demonstrates a facile, metal-free, and “greener” alternative to preparing acrylic diblock copolymers of polyethylene (PE). Diblock copolymer architecture was substantiated via analysis of 1H NMR spectroscopic, UV-GPC chromatographic, DSC onset crystallization (Tc), and MALDI-ToF mass spectrometric data. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3326–3335

Grafting of N,N-dimethylaminoethyl methacrylate from PE/PP nonwoven fabric via radiation-induced RAFT polymerization and quaternization of the grafts

Radiation induced grafting method is one of the most promising grafting techniques and it works successfully together with the reversible addition fragmentation chain transfer (RAFT) polymerization, one of the most prominent controlled free-radical polymerization (CRP) methods. This study reports grafting of N,N-dimethylaminoethyl methacrylate (DMAEMA) from the surface of polyethylene/polypropylene nonwoven fabric (PE/PP NWF) by the combination of radiation-induced initiation and the RAFT polymerization technique. Effects of monomer concentration, absorbed dose and solvent choice on the grafting yield have been investigated. The grafted NWF's were characterized by ATR–FTIR, XPS, SEM, EDX and thermal analysis methods. The results indicated that surface properties were completely altered after grafting compared to pristine PE/PP even for those with very low degree of PDMAEMA grafting. Free homopolymers in solution have been analyzed by GPC in order to obtain information about the grafts. The PDMAEMA grafts on the fabric surfaces were later quaternized with dimethyl sulfate to yield positively charged surfaces that were tested for antibacterial properties.

ChemInform Abstract: A Guide to the Synthesis of Block Copolymers Using Reversible‐Addition Fragmentation Chain Transfer (RAFT) Polymerization

AbstractReview: 50 refs.

A guide to the synthesis of block copolymers using reversible-addition fragmentation chain transfer (RAFT) polymerization

The discovery of reversible-deactivation radical polymerization (RDRP) has provided an avenue for the synthesis of a vast array of polymers with a rich variety of functionality and architecture. The preparation of block copolymers has received significant focus in this burgeoning research field, due to their diverse properties and potential in a wide range of research environments. This tutorial review will address the important concepts behind the design and synthesis of block copolymers using reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT polymerization is arguably the most versatile of the RDRP methods due to its compatibility with a wide range of functional monomers and reaction media along with its relative ease of use. With an ever increasing array of researchers that possess a variety of backgrounds now turning to RDRP, and RAFT in particular, to prepare their required polymeric materials, it is pertinent to discuss the important points which enable the preparation of high purity functional block copolymers with targeted molar mass and narrow molar mass distribution using RAFT polymerization. The key principles of appropriate RAFT agent selection, the order of monomer addition in block synthesis and potential issues with maintaining high end-group fidelity are addressed. Additionally, techniques which allow block copolymers to be accessed using a combination of RAFT polymerization and complementary techniques are touched upon.

Thermomechanical Properties of Bimodal Brush Modified Nanoparticle Composites

The enthalpic incompatibility of organic polymer matrices and high surface energy inorganic nanoparticles often leads to phase separation in polymer nanocomposites (PNC) precluding the realization of anticipated property enhancements. The grafting of polymer chains to nanoparticles holds promise as a means for controlling dispersion. A single population of polymer chains with tunable graft density (σ) and molecular weight (N) is observed to have antithetical enthalpic and entropic effects on interface compatibility. We report the use of bimodal polymer brushes with fundamentally decoupled enthalpic and entropic parameters. Bimodal polystyrene brushes were grafted from 15 nm colloidal silica nanoparticles by a previously reported consecutive RAFT (reversible addition–fragmentation chain transfer) polymerization technique. The combination of a high graft density short brush and a low graft density long brush was found to cause improved nanoparticle dispersion in a polystyrene matrix when compared to single populations of long and short brushes of corresponding graft densities and molecular weights. A new quantitative model was developed to understand these results and was found capable of predicting dispersions in grafted nanoparticle composites in the allophobic dewetting regime. The bimodal-brush-graft particles were also found to be remarkably well dispersed in an entropically unfavorable higher molecular weight matrix. This facilitated a study of the role of matrix–brush entanglement on the thermomechanical properties of PNCs, isolated from the effects of particle dispersion. The best enhancements in glassy properties resulted from improved matrix–brush entanglement, attained by lowering the long chain graft density and increasing the long chain to matrix molecular weight ratio.

Synthesis and Characterization of Dye-Labeled Poly(methacrylic acid) Grafted Silica Nanoparticles

The synthesis of dye-labeled poly(methacrylic acid) (PMAA) grafted silica nanoparticles was studied. Surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of tert-butylmethacrylate (tBuMA) was conducted on dye-labeled CPDB coated silica nanoparticles followed by sequential removal of the thiocarbonylthio end groups and the tert-butyl moieties. Additionally, as a more straightforward strategy, direct polymerization of methacrylic acid on silica nanoparticles with a diameter size as small as 15 nm was conducted via the RAFT polymerization technique. A variety of PMAA brushes with different lengths and densities were prepared on nanoparticle surfaces via surface-initiated RAFT polymerization with excellent control and surface grafting densities as high as 0.65 chains/nm2. The grafted PMAA was methylated by trimethylsilyldiazomethane to conduct organic phase GPC characterization. The dye-labeled PMAA grafted nanoparticles provide a platform to bind biomolecules and to track the movement of the nanoparticles in biological systems.

Preparation of clenbuterol imprinted monolithic polymer with hydrophilic outer layers by reversible addition–fragmentation chain transfer radical polymerization and its application in the clenbuterol determination from human serum by on-line solid-phase extraction/HPLC analysis

A novel imprinted monolithic material with the ability of protein exclusion was developed for the selective extraction of clenbuterol (CLE) from biological samples by direct injection in the HPLC analysis. The material has an imprinted inner structure and hydrophilic outer layer. The reversible addition-fragmentation chain transfer (RAFT) polymerization was employed in the material preparation by a two-step procedure. In the first step, clenbuterol imprinted monolithic polymer was synthesized by combining the molecular imprinting and the RAFT polymerization techniques. The resulting monolithic polymer has a RAFT chain transfer agent (trithioester groups) in its structure, which was used to graft poly(glycerol mono-methacrylate) [pGMMA] in the second step by post-RAFT polymerization. The hydrophilic pGMMA layers grafted on the surface of the imprinted monolith created barriers for protein diffusion. More than 90% of bovine serum albumin can be excluded from the pGMMA coated monolithic column. Meanwhile the clenbuterol was retained selectively with a large retention factor. The result indicated that the column, denoted as RA-MIM, has both the merits of a molecularly imprinted polymer and restricted access material. By using RA-MIM as the solid-phase extraction pre-column, an on-line column-switching HPLC method for the determination of clenbuterol in human serum has been established and validated. The recoveries of clenbuterol from the serum were 87.3-96.9% in the spiked level 2-1000 ng mL(-1). Both good linearity (R = 0.999) and acceptable reproducibility (RSD < 7.0%) were obtained. The limit of detection and the limit of quantitation were 0.7 ng mL(-1) and 2.0 ng mL(-1) respectively, which is sensitive in terms of UV detection. The results have demonstrated that the RAFT polymerization can be used to synthesize bi-functional monolithic columns by using its living reaction property. The resulting RA-MIM in this research can be used for efficient clenbuterol determination by HPLC from biological samples.

Polymerization of free secondary amine bearing monomers by RAFT polymerization and other controlled radical techniques

AbstractThis work describes the polymerization of the free secondary amine bearing monomer 2,2,6,6‐tetramethylpiperidin‐4‐yl methacrylate (TMPMA) by means of different controlled radical polymerization techniques (ATRP, RAFT, NMP). In particular, reversible addition‐fragmentation chain transfer (RAFT) polymerization enabled a good control at high conversions and a polydispersity index below 1.3, thereby enabling the preparation of well‐defined polymers. Remarkably, the polymerization of the secondary amine bearing methacrylate monomer was not hindered by the presence of the free amine that commonly induces degradation of the RAFT reagent. Subsequent oxidation of the polymer yielded the polyradical poly(2,2,6,6‐tetramethylpiperidinyloxy‐4‐yl methacrylate), which represents a valuable material used in catalysis as well as for modern batteries. The obtained polymers having a molar mass (Mn) of 10,000–20,000 g/mol were used to fabricate well‐defined, radical‐bearing polymer films by inkjet‐ printing. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Styrenated sunflower oil polymers from raft process for coating application

AbstractOil‐based macroinitiator (MI) obtained from sunflower oil was styrenated using reversible addition–fragmentation chain transfer polymerization (RAFT) in the presence of phenacyl morpholine dithiocarbamate (PMDC) as chain transfer agent. The solvent effect and effect of the molar ratio of the transfer agent, PMDC, on polydispersity and molecular weight of the polymers were investigated. The obtained results showed that, 1,4‐dioxane is a better solvent and 1/4 molar ratio of [MI]/[PMDC] provides relatively low polydispersities. No homopolystyrene was detected under these conditions, indicating the efficiency of PMDC in the chain transfer process. Livingness of the polymerization process was confirmed by chain extension with styrene using the preformed polymer as macrotransfer agent. The film properties of styrenated oil samples were determined according to the related standards. To improve film properties, the polymer obtained by RAFT technique was modified by reaction with MI. The resulting material gave transparent films with good film properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The effect of polymer architecture, composition, and molecular weight on the properties of glycopolymer-based non-viral gene delivery systems

Although a variety of non-viral gene delivery vectors has been synthesized and used for gene delivery purposes, well-defined glycopolymer-based gene delivery carriers is not well explored. Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization technique allows successful and facile synthesis of cationic glycopolymers containing pendant sugar moieties in the absence of protecting group chemistry. A library of cationic glycopolymers of pre-determined molar masses and narrow polydispersities ranging from 3 to 30 kDa has been synthesized using RAFT polymerization technique. These polymers differ from each other in their architectures ( block versus random), molecular weights, and monomer ratios (carbohydrate to cationic segment). It is shown that the above-mentioned parameters can largely affect the toxicity, DNA condensation ability and gene delivery efficacy of these polymers. Statistical copolymers of high degree of polymerization are found to be the ideal vector for gene delivery purposes. These statistical copolymers show lower toxicity and higher gene expression in the presence and absence of serum, as compared to the corresponding diblock copolymers. This is the first example of well-defined synthetic glycopolymers as DNA carriers that works both in the presence and absence of serum proteins. The critical composition of carbohydrate segment in copolymers for enhanced gene delivery and low toxicity was determined and an increase in carbohydrate residues in copolymers resulted in a decrease in transfection efficiencies of these polymers. The effect of serum proteins on statistical and diblock copolymer based polyplexes and hence gene delivery efficacy was studied. The results showed that the diblock copolymer-based polyplexes showed lower interactions with serum proteins, lower cellular uptake and very low gene expression in both Hep G2 and Hela cells in comparison to statistical copolymers.

Production of oil-based binder by RAFT polymerization technique

In this study, air-blown linseed oil was styrenated by reversible addition–fragmentation chain transfer polymerization (RAFT). For this purpose, hydroperoxide groups were formed in the structure of linseed oil by blowing air through it. The oxidized oil was used as a macroinitiator in the styrenation process by RAFT technique using phenacyl morpholine dithiocarbamate (PMDC) as a RAFT agent. The obtained samples were characterized by GPC and FT-IR measurements. The effects of various parameters, such as the amount of PMDC, the number of peroxide groups, and the reaction time were investigated on polydispersity and molecular weight. For comparison, a copolymer sample was also prepared in the absence of PMDC. The film properties of all the samples were determined according to the related standards and compared. The sample obtained by the RAFT technique exhibited better film properties and a relatively narrow polydispersity, showing that the RAFT technique provides good control over the polymerization system in this study.

Synthesis of Surface-Initiated Stimuli-Responsive Diblock Copolymer Brushes Utilizing a Combination of ATRP and RAFT Polymerization Techniques

The synthesis of diblock copolymer brushes, including poly(styrene) (PSty)-b-PSty, PSty-b-poly(acrylic acid), PSty-b-poly(N-isopropylacrylamide), and poly(methyl acrylate)-b-poly(N,N-(dimethylamino)ethyl acrylate), was achieved utilizing a combination of surface-mediated atom transfer radical polymerization (ATRP) and reversible addition−fragmentation chain transfer (RAFT) polymerization techniques. Conversion of bromine end groups of homopolymer brushes formed by ATRP via a modified atom transfer addition reaction to a RAFT agent and diblock extension via RAFT polymerization allowed the direct formation of well-defined stimuli-responsive diblock copolymer brushes. The addition of sacrificial initiator and/or chain transfer agent permitted formation of well-defined diblock copolymer brushes and free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Ellipsometry, contact angle measurements...

Biodistribution and Pharmacokinetic Studies of Bone-Targeting N-(2-Hydroxypropyl)methacrylamide Copolymer−Alendronate Conjugates

The biodistribution and pharmacokinetics of bone-targeting N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-alendronate conjugates were evaluated following intravenous administration of radioiodinated conjugates to young healthy BALB/c mice. The synthesis of a polymerizable and cathepsin K cleavable alendronate derivative, N-methacryloylglycylglycylprolylnorleucylalendronate, enabled the preparation of HPMA copolymer-alendronate conjugates with varying composition. Using the RAFT (reversible addition-fragmentation chain transfer) polymerization technique, four conjugates with different molecular weight and alendronate content and two control HPMA copolymers (without alendronate) with different molecular weight were prepared. The results of biodistribution studies in mice demonstrated a strong binding capacity of alendronate-targeted HPMA copolymer conjugates to bone. Conjugates with low (1.5 mol%) alendronate content exhibited a similar bone deposition capacity as conjugates containing 8.5 mol % of alendronate. The molecular weight was an important factor in the biodistribution of the HPMA copolymer conjugates. More conjugate structures need to be evaluated, but the data suggest that medium molecular weights (50-100 kDa) might be effective drug carriers for bone delivery.

Synthesis of Surface Initiated Diblock Copolymer Brushes from Flat Silicon Substrates Utilizing the RAFT Polymerization Technique

The synthesis of a variety of well-defined diblock copolymer brushes, including poly(methyl methacrylate) (PMMA)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), PMMA-b-poly(styrene) (PSty), and PSty-b-poly(methyl acrylate), was achieved via surface immobilized reversible addition−fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agents (CTAs) by utilizing a modified atom transfer addition reaction involving a silicon wafer modified with (11-(2-bromo-2-methyl)propionyloxy)undecyltrichlorosilane and dithiobenzoyl disulfide. Diblock copolymer brushes were then prepared via sequential surface initiated RAFT polymerization from the immobilized CTA. Various characterization techniques including ellipsometry, contact angle measurements, grazing angle attenuated total reflectance−Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the immobilization of CTAs on the silicon wafer and the s...

Synthesis of Narrow Polydispersity Block Copolymers of PtBA-PS by Novel RAFT Polymerization Technique

The synthesis of narrow disperse polystyrene (PS) and poly-t- butylacrylate (PtBA) was carried out by copolymerization using benzyldithiobenzoate as the chain transfer agent (CTA). Benzyl dithiobenzoate as a reversible addition-fragmentation chain transfer (RAFT) agent has high transfer coefficient in polymerization of styrene to produce PS with higher molecular weight than that of calculated, in contrary with polymerization of t- butylacrylate to produce PtBA. These results were attributed to instability the benzyl dithiobenzoate as RAFT agent under the reaction conditions. PS as a macro-CTA is not active for t-butylacrylate polymerization due to low transfer coefficient. On the other hand PtBA as the macro-CTA is active to polymerize styrene to produce PtBA-PS block copolymer with high transfer coefficient if PtBA as macro-CTA have narrow polydispersity. The RAFT agent appears to degrade over a period of time when it is left at room temperature, which was evident from the results of PtBA